The present invention relates to a method and a device for controlling the torque of a brushless DC motor used in an electric motorcycle. More particularly, a device in which a single current loop is applied to detect a feed-back current from a DC bus of the driver, and a torque command signal is input to generate the motor's positive torque, or a brake command signal is input to generate the motor's negative torque. The devices cause the brushless DC motor to stop when the electrical angle of reverse rotation of the motor becomes less than 120.degree..
Generally, a driver circuit of the motor used in an electrical motorcycle is so designed to provide simplicity, reliability and compactness; plus, an ability of restoring the energy generated during a braking operation into a battery of the motor is preferred.
Conventionally, a general-purpose brushless DC motor is so operated as torque control that 2 or 3 phase currents are used to perform a feedback control with 2 or 3 detectors in association with 2 or 3 low pass filters. The input signal supplied to torque controlling circuit is only an analog torque command which can be a positive or negative voltage signal and is supplied to a current compensator with a simultaneous current feedback signal therefore an analog torque command can generate positive or negative torque to rotate the motor in a clockwise or a counterclockwise direction.
In the case of a gas-powered motorcycle, the motor is adapted to generate a positive torque only to perform a forward rotation as gas is applied. Likewise, the electric motor to be controlled by the device of the invention is to rotate in a forward direction and the rotation in a reversed direction is prohibited.
The present invention has been accomplished under the aforesaid circumstances. The device of this present invention employs a single current loop to obtain a feedback control current signal from the DC bus by a detector, such that one shunt can be used in common for both a current feedback circuit and a current limiting circuit, as disclosed in a U.S. patent application Ser. No. 08/012,889, now U.S. Pat. No. 5,341,077 for METHOD AND DEVICE FOR LIMITING ELECTRIC CURRENT SUPPLIED TO THE MOTOR OF AN ELECTRIC VEHICLE. There are two signals input to the control torque circuit; one of them is a torque signal for generating a positive torque, and the other is a braking signal for generating a negative torque. When the motor is operated to generate a negative torque, it operates as a generator to produce an electrical power during a braking operation, and the produced electrical power is stored in the battery; it will stop when its angle of rotation becomes less than 120.degree. electrical angle (40.degree. mechanical angle for a 6-pole motor) in a reversed direction rotation, so that the electric motorcycle will not rotate backwardly.